Kinetics of interfacial radical polymerization initiated by a glucose-oxidase mediated redox system

Abstract

The reaction and coating kinetics for the glucose oxidase initiated interfacial polymerization are elaborated. The interfacial film grows rapidly and linearly with time, producing time-dependent controllable conformal coating thicknesses of up to a millimeter in less than 4 minutes. Bulk polymerization was only observed when the immersing media was stirred to induce higher mass transport rates. The dramatically different film thicknesses observed between different concentrations of glucose in the hydrogel and iron in the bulk media are demonstrated to be a result of an initial rapid growth phase following which the film grows at the same rate nearly independent of either the glucose or iron concentration. The polymerization rate and hence the thickness growth rate in this initial phase saturate at glucose and iron concentrations above 0.8 M and 0.63 mM, respectively. At iron concentrations above 0.05 mM, the film thickness at the end of 3 hours of reaction monotonically decreased with increasing iron concentration from 5.7 mm to 4.2 mm. The glucose oxidase is trapped by the growing polymerization front and can be used as the sole enzymatic precursor to coat a second polymeric layer. However, the rate of film growth of the second layer is 14-fold lower than the rate of film growth when bulk enzyme is present during the second stage coating process.

Interfacial Thiol-ene Photoclick Reactions for Forming Multilayer Hydrogels

“…The thiol-ene interfacial photopolymerization developed here is similar to the GOx-mediated coating system developed by Johnson and Bowman et al 20–22 and the interfacial PEG-diacrylate (PEGDA) photopolymerization system pioneered by Hubbell et al 3, 9, 28–30 The major differences between our system and the previous ones are two-fold: (1) our coating chemistry is a step-growth gelation mechanism, and (2) the macromer solution used in our thiol-ene interfacial coating procedures contained only macromers (i.e., PEG4NB and DTT) without additional co-initiator or co-monomer. Further, our controlled experiments demonstrated that this interfacial cross-linking was not due to initiator-free thiol-ene photopolymerization as gelation was not observed after prolonged light exposure (> 1 hour) without the presence of eosin-Y (data not shown).…”

“…The unique visible light-mediated interfacial thiol-ene gel coating system is comparable to the glucose oxidase (GOx) mediated gel coating system reported by Bowman and colleagues. 20–22 The GOx-mediated gel coating system, however, uses multiple initiator components (i.e., GOx, glucose, and ferrous ion) to initiate polymerization reactions. Because the process produces highly cytotoxic hydrogen peroxide (H 2 O 2 ), a second enzyme, catalase, has to be included in the macromer solution to prevent cellular damage.…”

A Comprehensive Kinetic Model of Free‐Radical‐Mediated Interfacial Polymerization

“…In our earlier investigation,5 we reported that glucose oxidase is trapped by the propagating polymerization front; however, the concentration of the active enzyme is significantly lower than the concentration of the bulk enzyme. This outcome arises as a result of inefficiency in encapsulation as well as inactivation of the enzyme by hydrogen peroxide where the inactivation by hydrogen peroxide has been extensively investigated in the literature 21–24.…”

“…However, one representative value for the enzyme fraction trapped is used for all experimental conditions. To obtain the values for these unknown constants, the model prediction for the time‐dependent thickness was fit to the experimental data reported earlier for two cases 5. In the first case, the enzymatic precursor for film formation is the glucose oxidase (GOx) in the bulk media (Figure 3a).…”

“…Subsequent immersion of the hydrogel into the aqueous phase results in rapid diffusion of glucose into the bulk media to initiate the polymerization reaction. Experimental work on this technique5 has investigated the factors that determine the degree of reaction delocalization and its influence on the kinetics of film growth. The model enables materials and process design with selection of appropriate monomers, initiating systems, and conditions necessary for optimization of this interfacial polymerization process.…”